Organochlorine Insecticides - PowerPoint Presentation

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Organochlorine Insecticides

Dr.

Kumari

Anjana

Assistant Professor

Deptt

. of Veterinary Pharmacology & Toxicology

Bihar Veterinary College, Bihar Animal Sciences University, Patn

a

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Contents of the chapter

Introduction to AgrochemicalsIntroduction to Pesticides

Pesticides ClassificationIntroduction to

Insecticides

Insecticides Classification

Organochlorine

compounds

Sources of poisoning

Classification of OCI

Factors affecting toxicity

Mechanism of Toxicity

Clinical symptoms

PM Lesions

Diagnosis

Treatment

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Agrochemicals

Agrochemicals are of two major groups:

Fertilizers Pesticides

Nitrate, Phosphorus and Urea are used as fertilizers.

A pest is an uneconomical, undesirable or harmful species that adversely affect the economic, desirable or beneficial species. Pesticides are used to kill the pests.

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Pesticides

Pesticides:are heterogeneous groups of substances used for preventing, destroying or repelling

pests.

Pesticides are the most widely used agrochemicals of toxicological importance.

Use – economical control of pests

or increase production of crops

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Insecticides

Organochlorines

Diphenyl aliphatic agentsChlorinated

cyclodienes

Arylhydrocarbons

Organophosphates

Phosphate

Phosphonate

Phosphorothionate

Phosphorothiolate

Carbamates Carbaryl propoxurPyrethrins and pyrethroidsNatural pyrethrinsSynthetic pyrethroids

Herbicides or weedicidesDinitrocompoundsPhenoxyacetic acidsBipyridium compoundsTriazenes RodenticidesInorganic agentsDicumarol derivativesGlycosidesFungicides ZinebCaptan FumigantsEthelene dibromide

Pesticides Classification

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Insecticides

Substances which are specifically used for preventing, destroying or repelling the insects pests.

The use of insecticides in agriculture has grown tremendously since world war II.

Now a days insecticides have become an integral part of agriculture.

Large scale use-

acute

toxicities,

residues in food stuff

and environmental problem.

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Organochlorines- DDT, BHC

Organophosphates- malathion,

sarin

Carbamates

-

Carbaryl, propoxur

Pyrethrins and pyrethroids-

allethrin, deltamethrin

Formamidine

insecticides-

amitrazNatural products- rotenone, nicotine, antibioticsInsecticides

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OrganochlorinesOrganochlorines

were the first major class of synthetic organic chemical to become widely used as insecticides.

Use- contact insecticides and

ectoparaciticides

.

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Sources of poisoning

Accidental ingestion of these products may lead to toxicity.

Environmental pollution. Residues

in agricultural products.

Consumption of

freshly sprayed crop

by animals.

Improper dilution in

sprays and dips

may cause toxicity.

Spillage of insecticides into food during storage or transport.Secondary poisoning in predator animals.

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Classification of OCI

Diphenyl aliphatic agents - DDT,

methoxychlor, perthane

,

dicofol

Hexachlorocyclohexane

–

Lindane

,

mirex, kepone, BHC Cyclodiene agents – Aldrin, dieldrin, chlordane, endrin, endosulpahan

, toxaphene heptachlor

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1874 : Dichloro diphenyltrichloro ethane (DDT) was synthesized. 1939 : Its insecticidal property was discovered by Paul Muller.

1948 : Paul Muller, a Swiss chemist who was awarded Nobel prize for his contribution.

However its effectiveness in controlling pests was short lived due to its persistence in the environment for a prolonged time.

It is also stored in the body fats of animals which is eliminated at extremely slow rate and has biomagnifications potential.

One of the most adverse effects of DDT due to biomagnifications is the decline in the population of certain

birds due to thinning of their egg shells.

Because of its persistence in the biosphere, the use of DDT has been banned by almost all the countries including India.

Dicofol

and

methoxychlor

are still in use. DDT

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Chemical structure of OCI Presence of cyclic carbon chain.

Apolarity and

lipophilicity.

Chemical unreactivity and

high stability in the environment.

T

½ of

OCl

in soil - 1-12 years.

T ½ of DDT in soil -- 3-10 years

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Factors affecting toxicity

Young animals- more sensitive.

Female- more sensitive.

Fatty and lactating animal-

more sensitive.

Stress and illness

enhance the toxicity.

More toxic in oily vehicle

then suspension and dry powder.

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Cyclodiene group- more toxic

Oral LD50 - 5- 100 mg/kg cattle.

DDT group -

least toxic

Oral LD

50 -

250-1000 mg/kg cattle.

Cats

are more susceptible – other domestic animal.

Fish > mammal > birds.

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Properties of toxicological importance

Lipid soluble compound +Highly persistent in the environment

Bioaccumulation

upward in food chain from environment to animal or human hosts

.

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Toxicokinetics

OCIs are highly lipid soluble, so readily absorbed from skin and mucous membrane (accumulate in the body fat).

Asoption:

Its absorption from GIT is poor except in oily solution.

OCIs are not highly volatile – no inhalation

toxicosis

.

But aerosols can be absorbed.

After absorption - in blood stream bind with serum lipoprotein and stored in body fat.

Organochlorines are distributed to vital organs namely liver, kidney and brain.

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Metabolism:Metabolism

is mainly by liver and the metabolite may be non toxic than the parent compound.

Slow metabolism from deposited fat.

Excreted

Excreted

mainly in the faeces (unchanged form).

From body excreted in bile, urine and in lactating animals, it is excreted in milk.

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Mechanism of Toxicity

These drugs are

neurotoxic.

Diphenyl

OCI

E

asily enter in the nerve membrane interfere with

Na

+

Channel kinetics.

Prolong the time of sodium channel opening during depolarization.Sodium inflow is enhanced and potassium outflow is inhibited.Results in enhanced action potential and increased neuronal excitability (seizures).

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Cyclodiene and aryl hydrocarbon

Bind to a site close to ion channel on GABAA receptors.

Inhibit the binding of Inhibitory NT GABA to the receptor.

No opening of chloride channels. 

Partial

repolarization

of the neuron and a state of

uncontrolled excitation

.

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Clinical symptoms

Initial stimulation of CNS followed by depression and death due to respiratory failure.

Behavioural

symptoms-

like anxiety, aggressiveness, abnormal posturing, jumping over unseen objects, wall climbing and madness syndrome.

Neurological symptoms

- hypersensitivity to external stimuli, fasciculation and twitching of facial and eyelid muscles, spasm and twitching of the fore and hind quarter muscles, champing of the jaws, seizures and hyperthermia.

Cholinergic symptoms

- vomiting, marked salivation, mydriasis, diarrhoea and micturition are noticed.

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PM Lesions carcass – bruised, lacerated and dirty.

Rigor prominent.Chronic case- carcass emaciated and devoid of body fat. 

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Diagnosis

Acute toxicosis is diagnosed based on history of exposure, appropriate clinical signs.

Brain concentration is better then body fat diagnosis of acute

toxicosis

.

Half of the frozen

brain

should be submitted for analysis.

The other half should be fixed for histopathology to rule out infectious degenerative, or

neoplastic

diseases.To determine sources, specimens for analysis such as: feed, suspected insecticidal formulation - granules, liquid, old containers, etc., gastrointestinal tract contents and liver.

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TreatmentDiazepam,

phenobarbital or pentobarbital in dogs.

Thiobarbitone in cats Chloral hydrates, Phenobarbital or pentobarbital in

farm animals

.

Activated charcoal

(1-2g/kg).

If exposure is by dermal suspected, scrubbed (bathe) the animal with soapy water.

Supportive and symptomatic therapy.

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Methoxychlor

It is the only insecticide of DDT group which is still in use and is safest among the subgroup.The substitution of CH

3O (methoxy

) groups for chlorines renders the insecticide biodegradable and environmentally non- persistent.

As such, it retains some of the advantages of DDT but without most of its disadvantages.

It is stored in adipose tissue to about

0.2% of the extent of DDT,

and hail-life in rats is only about 2 weeks (DDT=6 months).

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Thank You